Introduction to Ranking Factors

To fully understand the process of search engine optimisation it is necessary to have some understanding of the factors that influence search engine ranking position.  This article describes some of the major factors that influence position, and is intended to provide some background information that will help you to understand the basic principles behind our approach to optimising a web site for search engine performance.

It should be noted that there are a very large number of factors that influence where individual pages are returned in search engine results.  Google claim to take into account over 100 different factors, others claim more, and of these factors there is no single “magic bullet” that will catapult a page or site up the rankings.  Consequently the process of search engine optimisation of necessity involves applying “best practice” principals to all aspects of a website: content organisation, structure, coding, and content, as well as the more commonly acknowledged metatags.  This article does not cover the detail of all these various factors, but is intended to provide an overview of the topic, highlighting the key aspects relevant to most site owners.

The factors which determine where a page will appear in search engine results largely fall into two groups: “on the page” relevancy factors, and “off the page” popularity factors.

“On the page” factors influence what priority the search engines give to particular key terms contained in the page, their frequency and placement. The “off the page” factors relate to the popularity of the page, most commonly viewed in the context of links, both internal links within the site and those from external sources.  These popularity factors are generally referred to as Page Rank factors (actually a proprietary Google term).  In addition to links, there are other popularity measures that search engines take into account, for example, click popularity and domain age, which are simple measures for search engines to identify.  However most of these other measures are extremely difficult if not impossible to influence, apart from providing proper titles and descriptions which encourage searchers to select your site in the search results as opposed to a competitor.

All major search engines predominantly use a combination of these two sets of factors to determine the final Search Engine Result Position (SERP).

In simple terms, the “on the page” factors determine whether a particular page will be selected for display in the results of a search for a given search term, and provide a basic ranking order correlating to the relevance of the text to the search term used.  Priority is given to exact phrase matches (including plurals), then words in the same order, followed by words out of order.

Placement of key terms is also important; in approximate descending level of importance: <title> tag, <h> tags, highlighted text, body text (density and distribution through text), and meta description.

Meta keywords have largely become irrelevant to search engines these days.  As keywords are hidden within the code it is too easy to use them to mislead (or “spam”) the search engines by their misuse.  Consequently, the major search engines attach little or no value to the keyword metatag.

Because assessing the relevancy of pages by the “on page” factors inevitably results in a huge number of pages with the same or highly similar relevancy scores, Google developed its Page Rank ranking system, a concept that has also been adopted and applied to a varying degree by the other search engines.

The idea behind Page Rank is rooted in the academic principal of cross citation, where papers on particular topics tend to reference many of the same sources.  Those sources quoted most often are viewed as “authority” sources, and are thus supposedly more important.

In the search engine environment this means that pages with more incoming links (citations) are viewed as more important, and this fact reflected in search results.  Initially the manner in which Page Rank was employed resulted in attempts at wholesale manipulation of results through the use of illegitimate linking strategies by so called “Black Hat” search engine optimisation firms.  But more recently the search engines have become more sophisticated in the interpretation of links, with a much greater emphasis on the relevancy of links, i.e. credit is given where links are between pages “on topic”, but links from dissimilar pages are either discounted or ignored, even penalised if they come from an identified “link farm” or “spam” site.

It should be remembered that search engines deliver individual pages in their results, not sites, but links are more frequently to the homepage of a site.  The Page Rank algorithm contains a mechanism for transferring the value of the Page Rank to other pages within the domain, effectively distributing some of the Page Rank value within the site.  This element of the algorithm has particular implications when designing the architecture of sites.

Page Rank is influenced by both internal and external links.  Part of the reason for this is to give an additional weighting to pages from within an “authority” site.  An authority site is one which features both a high level of Page Rank from external links, and which the search engines see as having a substantial number of pages relating to a particular topic.

Because part of the Page Rank value for any given page arises from the number of relevant inbound links, including internal site links, it can be seen that larger sites with clusters of related and relevant pages (“thematic clustering”) have the ability to induce Page Rank, and this can be witnessed in large information sites whose pages rank well but have lower numbers of external incoming links than might otherwise be expected.

The type of linking site may also affect the weighting of the Page Rank on an incoming link.  Domains with suffixes such as .ac (academic institution), .org (non profit organisation, and .gov (government organisation) are commonly believed to have more value, but since the evidence to support this is largely empirical, this might just be because such sites tend to be more extensive and contain more content relevant to any given topic.

These Page Rank factors are used to a greater or lesser degree, depending upon the search engine, to determine the final order of results.  It is important to remember that to achieve a good overall search engine position, pages must generally score well on both off the page and on the page factors, not just one or the other.

The weighting given to the Page Rank value differs between search engines; Page Rank is currently a major factor in Google results (some would argue a disproportionate factor), but appears to be of less importance with results based on the Yahoo, Inktomi and MSN indexes where “on the page” relevancy factors have greater influence.

It should also be noted that the Google Page Rank value is not just the single 1-10 number shown in the Google toolbar and by other online tools.  The Page Rank formula and its true results are a very closely guarded secret, and the displayed Page Rank is only very broadly derived from it; Google themselves have described the Page Rank displayed on the toolbar as a “toy”.

Summary 

So, in summary: the final search engine position of an individual page will be established by several principal factors:
•    The relevancy of the page to the search term,
•    The Page Rank value determined from the internal links within the domain,
•    The Page Rank value determined by any inbound links directly to the page, plus a shared value relating to the accumulation of inbound links acquired by the domain as a whole
•    The Page Rank value determined through the net value of outbound links
•    Any additional popularity factors such as click popularity or domain weighting.

In practical terms, this means that optimising a site for the search engines is a combination of both optimising individual pages around the key relevant “on the page” factors, and ensuring that the site navigational and linking structure maximises the site’s Page Rank factors.